(1) Field of the Invention
The present invention relates to therapeutic medical apparatus, systems, devices and/or methods, and more particularly, to apparatus and methods for using neural stimulation to alleviate the symptoms of movement disorders, such as those associated with Parkinson's disease, essential tremor, dystonia, and Tourette's syndrome, including tremor, bradykinesia, rigidity, gait/balance disturbances, and dyskinesia.
(2) Technology Review
A current trend in the treatment of diseases identified as being associated with the central nervous system is the stimulation of target areas of the central nervous system to effect therapeutic benefit. Such stimulation has been accomplished with, for example, implanted electrodes that deliver electrical stimulation to target brain regions; one class of electrical neural stimulation devices has been categorized under the name “deep brain stimulation” (DBS). Although the exact neurological mechanisms by which DBS therapies succeed are complex and are not yet fully understood, such therapies have proven effective in treating Parkinson's disease motor symptoms (such as tremor, bradykinesia, rigidity, and gait disturbances), and investigation into the use of DBS for the treatment of this and other neurological and mental health disorders, including major depression, obsessive-compulsive disorder, tinnitus, obesity, criminal tendencies, and antisocial disorders, is ongoing.
Typically, medication for Parkinson's disease (PD) consists of Levodopa to alleviate symptoms. Over time, however, the medication has reduced efficacy and shows increased occurrence of side effects such as dyskinesias. Once side effects outweigh benefits, patients consider deep brain stimulation (DBS). An electrode/wire lead is implanted in a specific location in the brain which shows hyperactivity in PD patients and is sensitive to electrical stimulation. PD target sites are the subthalamic nucleus (STN) or globus pallidus internus (GPi). The Essential tremor and Parkinson tremor target site is generally the ventral intermedius nucleus of the thalamus (VIM). Electrical pulses characterized by amplitude (volts), current (amps), frequency (Hz), and pulse width (microseconds) are regulated by an implantable pulse generator (IPG) placed beneath the skin on the chest. Stimulation affects motor symptoms on the contralateral side, i.e., right side tremor will be treated on the left brain. After a patient has been implanted and recovered, programming sessions will fine tune stimulation settings described above in order to minimize symptom severity, minimize side effects, and maximize IPG battery life span. Although medication is not eliminated, it is typically reduced significantly. DBS efficacy decreases over time as the body adjusts to stimulation and protein buildup around electrode lead attenuates electrical field. Programming sessions are required throughout the patient's lifetime, though the frequency of adjustments are typically greater at first.
A typical implanted DBS stimulation lead consists of a thin insulated needle comprising four platinum/iridium electrodes spaced 0.5 or 1.5 mm apart along the length of the lead. One or multiple leads may be implanted in a target brain region or regions to provide symptom-inhibiting high-frequency stimulation, although some research suggests that excellent results can be achieved even when the lead is implanted distant from a target region. A DBS lead is connected to an implantable pulse generator (IPG), which serves as a controller and power source, via an extension cable tunneled subcutaneously to a subcutaneous pocket in the chest or abdominal cavity. The IPG typically includes a battery and circuitry for telemetered communication with an external programming device used to adjust, or “tune,” DBS lead stimulation parameters, which may include stimulation frequency, amplitude, pulse width (or wavelength), and contact configuration (that is, the selection of which electrodes are utilized from among the four electrodes available on a lead, and, if two or more electrodes are active, the relative polarity of each). These parameters are initially set during implantation surgery and are then further fined-tuned in the outpatient clinic or in a doctor's office following surgery to maximize therapeutic benefit and minimize undesirable stimulation-induced side effects. The first such tuning session usually takes place several weeks following implantation surgery, after the patient has recovered and inflammation at the lead placement site has subsided.
While the above-described equipment and procedures are typical as of the filing of this application, variations and refinements may become commonplace as neural implant technology advances. Conceivably, uses of a multiplicity of DBS leads or networks of DBS leads may provide greater coverage, enabling the stimulation of larger and more varied target areas, and miniaturization and improved telemetry may obviate the need for the extension cable and/or the IPG altogether as leads become self-powering and/or self-controlling or permit for built-in telemetry. Advances in nanotechnology and materials may also allow DBS leads in the future to become self-repositioning, self-cleaning, or resistant to biological rejection for improved long-term therapeutic operation and more precisely targeted implantation.
The current standard in evaluating the severity of movement disorder symptoms in Parkinson's disease is the Unified Parkinson's Disease Rating Scale (UPDRS) used to score motor tests, many of which involve repetitive movement tasks such as touching the nose and drawing the hand away repeatedly, or rapidly tapping the fingers together. A battery of exercises, typically a subset of the upper extremity motor section of the UPDRS, is normally completed during DBS lead placement surgery and subsequent programming sessions to evaluate performance while a clinician qualitatively assesses symptoms. Each test is evaluated by a clinician based solely on visual observation and graded on a scale that ranges from 0 (insevere) to 4 (severe).
During DBS implantation surgery, various lead placement strategies are used, including inversion recovery imaging, reformatted anatomical atlases, and formula coordinates based on known landmarks. Implantation location is verified and adjusted based on electrophysiological mapping using techniques such as microelectrode recording and micro and macro stimulation. Currently, lead placement and stimulation parameters are modified based on subjective motor examinations such as clinical observation such as the UPDRS motor tasks during the implantation procedure. After lead placement, patient motor symptoms are evaluated in response to a set of stimulation parameters. Stimulation parameters are then adjusted, and motor exam repeated. This trial-and-error process of adjusting parameters and monitoring patient response is continued until an optimal electrode position and stimulation set are established. During this programming or “tuning” process, the clinician subjectively assesses motor symptom improvement.
Postoperatively, assessing DBS response and reprogramming stimulation parameters require a significant time commitment. Several stimulation parameters can be modified, including electrode polarity, amplitude, current, pulse width, and frequency. DBS programming and patient assessment may be performed by a variety of healthcare professionals, including movement disorder neurologists, neurosurgeons, fellows, occupational and physical therapists, and nurses. Stimulation optimization must be performed based on results of an exam such as the UPDRS, with the patient in four states (off medication/off DBS, off medication/on DBS, on medication/off DBS, and on medication/on DBS) per the Core Assessment Program for Surgical Intervention Therapies in Parkinson's disease (CAPSIT-PD) protocol. The process of DBS adjustment is iterative and largely involves trial-and-error. Retrospective studies have found that DBS programming sessions take more than twice as long as typical evaluations by movement disorder neurologists. Programming sessions are typically limited to 1-3 hours since longer sessions result in patient fatigue or lightheadedness. Programming and patient assessment from preoperatively to one year after surgery requires approximately 30 hours of nursing time per patient.
Clinicians presently lack tools that combine physiological, electrical, and behavioral data to optimize electrode placement and stimulator programming. Optimizing electrode placement and stimulation parameters improves patient outcome by alleviating motor symptoms and minimizing complications. The present invention addresses this need for improved electrode placement and adjustment of deep brain stimulation parameters by providing a repeatable, automated or semi-automated tool that can assist stimulation parameter tuning during surgical electrode placement and outpatient programming sessions. In particular, the present invention aims to provide methods for the collection and transmission of objective biokinetic data during these procedures, which data is then processed to output objective movement disorder symptom severity measures on a continuous scale in real-time to guide clinician decision making. The improved resolution and repeatable results of the present invention should reduce time and costs of DBS procedures as well as improve patient outcomes.
It is therefore the object of the present invention to couple automatically-assigned quantitative motor assessments with procedures and practices for DBS implantation and parameter tuning in semi-automatic and automatic ways to provide improved and less costly movement disorder patient therapy.
Existing systems for quantifying Parkinson's disease motor symptoms are described in this application's parent application, U.S. patent application Ser. No. 12/250,792, which is herein incorporated by reference, and which describes a novel system for measuring motor dysfunction symptoms and computing measures based on UPDRS scores therefrom. Preferably, the system and methods described therein are incorporated, in whole or in part, into the present invention as a means of automatic symptom quantification. The resultant scores objectively quantify movement disorder symptoms advantageously using a scale that is familiar to clinicians.